The present invention relates to thermoplastic polyesters having improved impact properties and to impact-modifier compositions.
Thermoplastic polyesters, such as PBT (polybutylene terephthalate) and PET (polyethylene terephthalate) possess excellent dimensional-stability, heat-resistance and chemical-resistance properties and are used in the electrical, electronic and motor-vehicle fields. However, at high temperature, during conversion operations, a reduction in the molecular weight of the polymer may occur, leading to a reduction in the impact properties. In addition, polyesters have poor fracture-resistance properties in the case of notched components.
The present invention provides thermoplastic polymers in which an impact-modifier composition is added in order to obtain improved impact properties, especially low-temperature toughness. The present invention also relates to this impact-modifier composition that is added to the polyesters to improve the impact properties thereof. These modifier compositions make it possible to achieve impact properties superior to those obtained with each of the compounds separately.
U.S. Pat. No. 4,753,890 (=EP 174,343) describes polyesters, such as, for example, polyethylene terephthalate (PET) or polybutylene terephthalate (PBT), which are modified by ethylene-alkyl (meth)acrylate-glycidyl (meth)acrylate copolymers.
U.S. Pat. No. 5,369,154 describes PET/polycarbonate blends containing four different modifiers: a copolymer comprising an epoxide, a copolymer of the core-shell type, an SBR- or SBS- or EPR-type elastomer and a copolymer of the SAN or ABS type. These core-shell copolymers comprise fine particles having an elastomer core and a thermoplastic shell.
Patent EP 115,015 describes PET or PBT containing linear low-density polyethylene (LLDPE), glass fibres and optionally a core-shell copolymer.
Patent EP 133,993 describes PET containing a core-shell copolymer and a copolymer of ethylene with either an alkyl acrylate or (meth)acrylic acid.
Japanese Patent Application JP 01,247,454 A, published on 3 Oct. 1989 describes PBT containing an ethylene-alkyl (meth)acrylate copolymer and an ethylene-glycidyl methacrylate copolymer.
Patents EP 838,501 and EP 511,475 describe compositions similar to those of the above Japanese application.
Patent EP 803,537 describes PET and polycarbonate containing a copolymer comprising glycidyl methacrylate. Firstly, the polycarbonate and the copolymer comprising glycidyl methacrylate are blended together and then this blend is incorporated into the PET.
Patent EP 187,650 describes PET containing a core-shell copolymer and a copolymer of ethylene with either maleic anhydride or a (meth)acrylic acid.
Patent EP 737,715 describes PBTs modified by an impact modifier consisting of an ethylene-methyl methacrylate-glycidyl methacrylate copolymer/core-shell copolymer blend. The amount of impact modifier is from 5 to 20 parts per 100 parts of polyester, i.e. 4.8 to 16.7% for 95.2 to 83.7% of polyester, respectively. The proportions of the glycidyl methacrylate copolymer to the core-shell copolymer are in the ratio 15/85 to 20/80. In the examples, the amount of impact modifier is from 18 parts per 100 parts of polyester, i.e. 15.3%, and the proportion of glycidyl methacrylate copolymer to the core-shell copolymer is in the ratio 3/15, i.e. 17/83.
Patent EP 531,008 describes spent (recycled) PBT/polycarbonate (PC) blends containing core-shell copolymers, to which functionalized copolymers are added in order to make them into a new thermoplastic. These functionalized copolymers are either ethylene-glycidyl methacrylate (GMA) copolymers or ethylene-vinyl acetate-glycidyl methacrylate copolymers. The description quotes proportions of 1 to 97% of polycarbonate, from 1 to 97% of PBT, 1 to 40% of core-shell copolymer and 1 to 40% of glycidyl methacrylate copolymer. In fact, the PBT/polycarbonate blends that it is desired to recycle contain, according to the examples, 15% of core-shell copolymer, which corresponds to more realistic values. Blends (i) of 80 parts of recycled material with 20 parts of glycidyl methacrylate copolymer and blends (ii) of 90 parts of recycled material with 10 parts of glycidyl methacrylate copolymer are then made. The proportions are in the EP 531,008 table below, in which the parts are by weight: